Traditionally, handsaws for the rip-sawing of wood in the direction of the grain have been made with raker teeth having crosswise edges approximately perpendicular to the saw blade surfaces, at least before setting of the teeth. On the other hand, handsaws for the cross-cutting of wood across the grain have been made with scratcher teeth having lateral edges formed by filed or ground bevels along the tooth contour and sharp points which severe the fibers like knife points.
For mixed use, i.e., for sawing of wood with variable grain direction and for sawing of plywood, particle board or similar sheet materials, both types of said teeth are inefficient.
Saw makers tried early to make saws for mixed use with alternating raker teeth and scratcher teeth, as shown in Boynton U.S. Pat. No. 73,226; Alexander U.S. Pat. No. 3,716,916; and Kuklinski U.S. Pat. No. 4,802,396, where the scratcher teeth are set so that their points create the sides of a kerf wider than the saw thickness. The raker teeth are straight and serve to transport the chips and to loosen lengthwise fibers from the kerf bottom. The scratcher teeth are somewhat higher than the raker teeth to ensure that during cross-cutting, the fibers are severed before they are loosened by the raker teeth.
Other tried designs include saws with scratcher teeth of equal height but variable setting width so as to position the points in four rows, as disclosed in Stones et al U.S. Pat. No. 4,784,034. This was intended to make the chips, even in rip-sawing, small enough to be transported out from the kerf.
A type of tooth whose configuration lies somewhere between raker and scratcher teeth is the shaving tooth having a chamfered contour and a top surface which slants obliquely inwards and rearwards is known from Laney U.S. Pat. No. 1,167,801; Owen U.S Pat. No. 2,072,624; and Anderson, Jr. et al U.S. Pat. No. 3,374,815. That tooth is intended to be capable of producing a smooth kerf during the return stroke.
Experience shows that a saw blade for mixed use should have some scratcher teeth for acceptable work in cross-cutting. Scratcher teeth which are set to create the sides of the kerf are very easily damaged by nails or mineral grains. Since each scratcher tooth is self-feeding in the lateral direction, a straight cut requires symmetrical forces, whereby even small damage on one side of the tooth can cause the saw to make a crooked cut.
None of the above-mentioned tooth configurations will make an acceptable cut in an end grain surface. With each configuration it is difficult to start a new cut with precision, and to saw straight in knotty or uneven wood.